In Docker, migrate runs as root while data/ belongs to www-data, so a
planted data/admin_password symlink would make root overwrite its target.
Remove any existing path first and create the file with
O_CREAT|O_EXCL|O_NOFOLLOW (mode set via fchmod). install.sh's /tmp
fallback log is now created with mktemp instead of a fixed name.
- The generated admin password is written to data/admin_password (mode
0600) instead of being printed, so it no longer ends up in the install
log or `docker logs`. If the file cannot be written it is printed as
before, so the admin is never locked out.
- webvirtcloud.sh no longer echoes the generated SECRET_KEY.
- install.sh creates the install log with mode 0600.
